1. A. Schild:Proc. S.I.F., Course XX (New York, 1962), p. 69.
2. J. D. Anderson et al.: Jet Propulsion Labs. Report (1970);I. Shapiro: cited in ref. (3).
3. K. S. Thorne, C. M. Will andW. T. Ni: Cal-Tech preprint, 1971. See alsoConference on Experimental Tests of Gravitation Theories, held at California Institute of Technology, November 11–13, 1970 and theInternational Conference on the Evidence for Gravitational Theories, Copenhagen, May, 1971.
4. H. Yilaz:Phys. Rev.,111, 1417 (1958);Proc. S.I.F., Course XX (New York, 1962). p. 233.
5. H. Yilmaz: unpublished (1959); Lecture at Boston University (1969), to be published in the series:Boston Studies in the Philosophy of Science (New York, 1972).